Coating and annealing process for magnetic materials and coated article produced thereby



March 5, 1958 w. P. LANGWORTH-Y ,32

comma AND ANNEALING PROCESS FOR MAGNETIC MATERIALS AND COATED ARTICLE PRODUCED THEBEBY Original Filed Oct. 7, 1953 STEP 8 Heating I COO Coming FIG. 2.-

WILLIAM F. LANGWORTHY I ATTORNEYS Lominations Are Stamped \To Proper Shape And Cleaned INVENTOR mireds ates Patfl Q COATING AND ANNEALING PROCESS FOR MAG- NETIC MIATERIALS AND COATED ARTICLE PRODUCED THEREBY I Wiiliam P. Langworthyfl jhiladelphia, Pa.

14 Claims. (Cl. 148-122) This invention relates to a coating and annealing process for magnetic materials and to a coated magnetic material produced by the foregoing process.

This application is a division of my copending application Serial No. 384,616, filed October 7, 1953, now Patent No. 2,779,699, granted January 29, 1957, hearing the same title.

It is well known that magnet cores for use in alternating current machines, such as transformers, must be laminated in order to reduce eddy currents. Laminating the core is not eifective unless the laminations are insu-, lated from each other. Moreover, in order to secure best results the laminations must be annealed in, a high temperature hydrogen atmosphere. While the effect of insulating the laminations and annealing the material may be determined experimentally in the laboratory, it has been difficult to achieve low cost production processes capable of attaining results such as those proved possible by laboratory experiments. One difiiculty encountered in practice is that during the high temperature annealing step the laminations tend to stick and/or weld together. Another difficulty is attaining adequateexposure of the surfaces of the stacked laminations to the hydrogen annealing atmosphere or medium. Still another difi'iculty involves obtaining, in production at a low cost, a thin insulating coating on the surface of the laminations that will reduce eddy current losses without seriously increasing the thickness of the laminations. The principal object of this invention is to overcome the foregoing difiiculties.

Another object of this invention is to provide an improved process for producing coated laminations for electrical machines.

A still further object of the invention is to provide an improved coated lamination for use in electrical machinery.

Other objects and advantages of the invention will appear as this description proceeds.

Others have discovered, prior to my invention, that a coating of calcium oxide may be applied to a metal base by heating the metal base to a temperature of several hundred degrees Fahrenheit and spraying it with a solution of calcium nitrate. Other nitratesmay also be used. I make no claim herein to that process but I claim the series of steps including applying that process to produce an extremely thin film on a metallic base composed of material whose magnetic properties are improved by a high temperature (about 1000 F. to 2350" F.) hydrogen'anneal, and then exposing the coated material to such an anneal. The results achievedfby this combination of steps are that the high temperature of the annealing step drives oi the last traces of the water in the coating and thus improves it. The coating step improves the annealing step by providing a porous film during the annealing step which separates the laminations sufliciently to allow the hydrogen atmosphere to contact the magnetic material and by separating the laminations to a sufficient extent that they do not stick together. More monoxide and perhaps hydrocarbons.

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over, after the process is completed the resulting laminations have a very thin film that will insulate them from each other after they are placed into use.

Hydrogen is the preferred atmosphere or medium especially when the metal from which the laminations are stamped is one of the well known magnetic nickel alloys of iron, such as the permalloys. One of these contains approximately 50% nickel, while the remainder is essentially iron. Another is composed of 79% nickel, 4% molybdenum and almost pure iron to make up the remaining balance of almost 17%. These materials may be annealed in a medium consisting of pure dry hydrogen, or if desired to make the process less expensive, the medium may be cracked ammonia or any other desired mixture of hydrogen with nitrogen. Either of these media may be used in 'the annealing of the silicon containing magnetic alloys of iron, but to further decrease the cost of these materialsthey are often annealed in a so called burned-out-air medium, which may contain variable amounts of nitrogen, carbon dioxide, carbon Such anneals of the silicon-iron alloys are usually done at a maximum temperature in the range between about 1000 F. and 1800 F., a value of 1450 F. being most common.

The problems involved and the desirability of a coating for magnetic laminations are discussed in U. S. Patent 2,410,220 to William P. Langworthy, dated October 29, 1946. The present invention describes certain improvements upon the basic teachings described and claimed in that patent.

In the drawings:

Figure 1 illustrates one form of the process constituting my invention; 0

Figure 2 illustrates a coated lamination according to the invention;

Figure 3 illustrates a box of stacked laminations; and

Figure 4 is a sectional view taken along line 44 of Figure 3.

Referring now to Figure 1, step A involves stamping a lamination of suitable magnetic material to proper shape and heat cleaning it at 800 F. Other cleaning methods may, of course, be used. The material is of a type Whose magnetic properties are improved by annealing it in a high temperature hydrogen atmosphere. One such material is permalloy which is a well known steel having about 50% nickel therein.

Step B involves heating the laminations singly or in groups to a temperature preferably between 400 F. and 1200 F. The laminations are heated in a gas fired or electric oven. An electrical induction heater may also be used. If burning gas is used to heat the laminations the products of combustion should not be allowed to contact the laminations to avoid poisoning them. Step C involves passing the heated laminations one at a time through a mist or fog composed of a solution of calcium nitrate in anhydrous ethanol, hereinafter termed CNE. The mist'of CNE solution may be produced, for example, by directing a spray toward the passing laminations. Preferably the CNE solution is dilute. When the dilute mist strikes the hot laminations the CNE solution breaks down leaving a thin coating of a refractory metal oxide, CaO, on the surface of the laminations. The anhydrous ethanol evaporates carrying with it the nitrogen pentoxide, N 0 resulting from the breakdown of CNE to the metallic oxide. As the temperature of the lamination is well above the boiling point of the nitrogen pentoxide, it passes off as a gas. It is of course possible that the ethanol and the nitrogen pentoxide may react to form other compounds, but the important thing is the deposit of the metallic oxide on the laminations. The laminations remain at the aforesaid 400 to 1200 F. tempera ture during the coating operation. The chamber or zone in which the mist or fog is created may encounter an elevated temperature due to the heated laminations passing therethrough.

Step D involves stacking the laminations after they have cooled. Figure 3 illustrates howthe laminations may be stacked in atray preparatory for the annealing step. The tray has separatorsll and 12,- and the laminations are stacked in rows as shown in Figure 4. Preparatory for the annealing step a number of trays of the type shown in Figure 4 may be placed on top of each other. These stacks of trays, so to speak, are placed in a heated hydrogen atmosphere for purposes of annealing. Step E involves annealing the stacked laminations at a high temperature in an annealing atmos phere or medium. I In the case of permalloy, step E is carried out at 1800 to 2350 F. in a hydrogen atmos phere; In order for the annealing' to have maximum beneficial effect the'hydrogen gas must permeate'the' pores of the laminations. This is possible in the present case since the thin discontinuous coating separates the laminations enough to allow hydrogen to enter between the laminations. Moreover, the coating is rather spotty or discontinuous, thus allowing the hydrogen gas to actu- I ally contact a very large percentage of the total surface. The thickness of the coating and the extent of its coverage can be controlled somewhat by varying the concentration of the solution in step C and also by varying the time period that the laminations remain in the mist or fog of CNE solution.

The high temperature annealing step accomplishes the additional function of driving off any remaining water of crystallization in the coating and thus improving it.

When the laminations have been annealed they are ready for use in a transformer or other'electrical machine in the usual way. Figure 2 is an illustration of the final product. The thin coating of calcium oxide crystals insulates the laminations from each other. However, the coating is so thin that it does not substantially increase the height of a stack of laminations. In techeuropiurn, gadolinium, dysprosium, holm'ium, erbium,

thul-ium, ytterbium, and thorium.

Hence, step C involves a metal compound that breaks down when heatedand releases a compound (usually the oxide) of the metal. The startingmetallic compound should be in a solution or in essentially sub-colloidal (less than 0.5 micron size) form in the solvent or've-' hicle which is removed by one or more of the heating steps of the whole process.

In all cases, the process 18 workable when the metal oxide content of the solution is between 0.1% and 10% by weight, and the temperature in step 0 is suifieie'nt to cause the oxide to bond itself to the base metal, usually several hundred degrees.

The calcium oxide coating is an improvementover the prior art since it does not poisonor otherwise injure the magnetic materials.

Laminations produced by this process have an improved permeability of about 20% over laminations produced by present day prior art commercial processes. This is true over a wide range of fiux density, for example from 40 to 4000 gausses. In the prior art the permeability of staeksof laminations varied substantially more from the overall average than is true with the process herein claimed;

Moreover, the same size of tray will hold more laminations coated by my process than it will hold of prior art laminations since the coating is thinner. In fact it is 7 possible in some cases tomore than doublethe quantity of laminations that may be placed in an annealing furnace or container of. any given size. It has also been found that notwithstanding the increased number of laminations placed inthe tray the heat is conducted to the innermost parts of the tray quicker than in the prior art, this being due to the fact that the coating is thinner than in the prior-art. Hence, it is possible to carry out the process in a shorter time than has heretofore been customary.

While there have been described above what are pres- 1 ently believed to be'preferred forms of the invention, the

appended claims are intended to include all variations thereof which fallwithin the true spirit of the invention.

I claim to have" invented:

l. The process of producing coated laminations of ma terial whose magnetic properties are improved by a high temperatureannealing in a suitable medium which includes stamping a lamination of said material, heating the lamination, passing the heated lamination through a mist of a dilute solution of a metal nitrate in anhydrous ethanol, the heating being to adegree high enough that it will break down the'metal nitrate into the metal oxide, stacking the laminations, and annealing the stacked laminations at a temperature higher than the one to which the laminations were subjected during the hereinabove mentioned heating step, the annealing being carried out in the presence of an annealing medium.

2. The process of producing coated laminations of permalloy which includes stamping the permalloy lami'n'a'tions, cleaning them, heating the laminations, expos ing' the laminations While thus heated to a mist of a solutionof calcium nitrate in anhydrous ethanol, the heating being to a degree high enough that it will break downthe calcium nitra'te' into the metal oxide, stacking the laminations, and annealing the stacked laminations in a hydrogen medium at a temperature in the range of 1800 to 2350 F. I

3. The process definedin claim 2 in which the solution is so dilute and the time of exposure of the laminations to the solution is so short that the coating formed on the laminations is discontinuous and of a thickness less than 0.0005 inch.

4. The process of producing coated laminationswhich are com osed of material whose magnetic properties are improved by a high temperature annealing step which includes passing the laminations into' a heated zone, exposing the laminations while in said zone to a vehicle carrying a compound of calcium which breaks down under the heat prevailing in said zone and deposits a refractory metal oxide of. calcium on a surface of the laminations, and annealing the laminations at a still higher temperature".

5. The process defined in claim 4 in which the laminations are in the form of a stack during the annealing ste The process of producing coated laminations of material whose magnetic properties are improved by a high temperature annealing in a suitable medium which includes stamping a lamination of said material, heating the lamination to a temperature. passing the heated lamination through a mist of a dilute solution of calcium nitr'a'te in anhydrous ethanol while the lamination is at such a high temperature that the calcium nitrate in anhydrous ethanol will be broken down leaving a coating of calcium oxide bonded to the lamination, stacking the laminations, and annealing the stacked laminations at a temperature higher than the one to which the laminations were subjectedduringthe hereinabove mentioned heating step, the annealing being carried out in the presence of an annealing medium.

7. The process of producing coated laminations of permalloy which includes stamping the permalloy laminations, cleaning them, heating the laminations to a temperature in the range of 400 to 1200 F., exposing the laminations while thus heated to a mist of a solution of calcium nitrate, the temperature of the laminations while exposed to the calcium nitrate being so high that when contacted by the calcium nitrate the latter breaks down and leaves a coating of calcium oxide bonded to the laminations, stacking the laminations, and annealing the stacked laminations in a hydrogen medium at a temperature in the range of 1800 to 2350 F.

8. The process of producing coated laminations of material whose magnetic properties are improved by a high temperature annealing in a'suitable medium which includes forming a lamination of said material, heating the lamination, passing the lamination while in a heated state through a mist of a dilute solution of calcium nitrate, said heating step raising the lamination to such a high temperature that the heat of the lamination will break down the calcium nitrate mist which contacts it leaving a coating of calcium oxide bonded to the lamination, said mist being so dilute that the coating which is formed will be discontinuous, and annealing the coated laminations at a temperature higher than the one to which the laminations were subjected during the hereinabove mentioned heating step, the annealing being carried out in the presence of an annealing medium.

9. The process of claim 1 in which the metal nitrate is calcium nitrate.

10. The process of claim 1 in which the metal nitrate is magnesium nitrate.

11. The process of claim 1 in which the metal nitrate is zirconium nitrate.

12. The process of claim 1 in which the metal nitrate is aluminum nitrate.

13. The process of claim 1 in which the metal nitrate is titanium nitrate.

14. The process of claim 1, in which the medium in which the high temperature annealing step is conducted is hydrogen.

References Cited in the file of this patent UNITED STATES PATENTS 1,335,024 Peschko Mar. 30, 1920 2,243,849 Kratky June 3, 1941 2,314,565 Thompson Mar. 23, 1943 2,318,606 Goebel et al. May 11, 1943 2,327,002 Thompson Aug. 17, 1943 2,410,220 Langworthy Oct. 29, 1946 

1. THE PROCESS OF PRODUCING COATED LAMINATIONS OF MATERIAL WHOSE MAGNETIC PROPERTIES ARE IMPROVED BY A HIGH TEMPERATURE ANNEALING IN A SUITABLE MEDIUM WHICH INCLUDES STAMPING A LAMINATION OF SAID MATERIAL, HEATING THE LAMINATION, PASSING THE HEATED LAMINATION THROUGH A MIST OF A DILUTE SOLUTION OF A METAL NITRATE IN ANHYDROUS ETHANOL, THE HEATING BEING TO A DEGREE HIGH ENOUGH THAT IT WILL BREAK DOWN THE METAL NITRATE INTO THE METAL OXIDE, STACKING THE LAMINATIONS, AND ANNEALING THE STACKED LAMINATIONS AT A TEMPERATURE HIGHER THAN THE ONE TO WHICH THE LAMINATIONS WERE SUBJECTED DURING THE HEREINABOVE MENTIONED HEATING STEP, THE ANNEALING BEING CARRIED OUT IN THE PRESENCE OF AN ANNEALING MEDIUM. 